**3.2.1 Response model**

Response models of dry tensile strength, wet tensile strength and degradation period at α=0.05, were significant and the models were shown as equation 3-1, 3-2 and 3-3.

$$\begin{aligned} \text{y\_1=30.38+9.135\times10^{-3}\text{x}\_1 + 5.4\text{x}\_2 \cdot 1.52\text{x}\_3 &+ 0.067\text{x}\_4 + 0.94\text{x}\_5 \cdot 1.02\text{x}^2 - 0.64\text{x}\_4^2 - 1.15\text{x}\_5^2 + 1.14\text{x}\_1\text{x}\_4 + 0.02\text{x}\_5 \cdot 1.02\text{x}\_6 \\ 1.24\text{x}\_2\text{x}\_3 &+ 0.96\text{x}\_3\text{x}\_4 - 1.11\text{x}\_4\text{x}\_5 & (3-1) \\ \text{y}\_2 &= 13.81 - 0.36\text{x}\_1 + 2.47\text{x}\_2 - 0.35\text{x}\_3 + 0.62\text{x}\_4 + 1.43\text{x}\_5 \cdot 0.62\text{x}\_4 - 0.42\text{x}\_5 + 0.64\text{x}\_1\text{x}\_3 + 0.46\text{x}\_2\text{x}\_5 - 0.44 \\ \text{x}\_3\text{x}\_5 &+ 0.65\text{x}\_4\text{x}\_5 \end{aligned} (3-1)$$
 
$$\begin{aligned} \text{y}\_3 &= 34.95 + 0.22\text{x}\_1 + 3.59\text{x}\_2 + 0.017\text{x}\_3 + 0.5\text{x}\_4 + 2.33\text{x}\_5 \text{-1.12}\text{x}\_2 \text{-1.12}\text{x}\_2 \text{-1.32}\text{x}\_2 \text{-0.87}\text{x}\_2 \text{-0.87}\text{x}\_2^2 \\ &+ 1.67\text{x}\_3\text{x} + 1.41\text{x}\_4\text{x} \end{aligned} (3-3)$$

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#### Importance of various factors on response functions was shown in table 3-3. Source Importance Dry tensile strength (N) Wet tensile strength (N) Degradation period (D) Beating degree 1.645 1.046 0.905 Grammage 1.838 1.323 2.341 Rosin 1.094 1.333 0.931 Bauxite 1.344 1.951 2.099 Wet strength agent 1.526 2.839 2.253

**3.2.2 Analysis of importance of various factors on response functions** 

Table 3-3. Importance of each factor

276 Biogas

(b) part of film samples after 35 days

Fig. 3-2. Mulching degradable process in the different time during the period of degradation

The fibre film of biogas residue for degradation discovered that the appearance and performance of the samples changed a lot because of light, air temperature, air humidity, wind, rain and other weather factors, coupled with the soil temperature, humidity, combined effect of microorganisms. According to the observation, the degradation was divided into several stages, initially, the sample surface appeared holes or small cracks, called induction period of the film degradation; over time, holes and cracks gradually expanded, the edge glued to the soil surface, the role of soil microorganisms on the film samples increased, resulted in an increasing number of small holes, broken into fragmentation period of the film samples, the film samples effected by various types of micro-organisms would become increasingly thin, the mechanical strength decreased gradually, until the film entered into the fast degradation period of the samples. Especially, after rain, the increasing of air humidity and soil humidity would make mechanical strength of the samples decrease rapidly, so soil moisture is an important impact factor of the film

During degradation of the film, the dry tensile strengths were regularly measured, according to scatter, the trends of dry tensile strength (N) and date (d) were available, according to trend line, the time of dry tensile strength at zero of each group was estimated,

Response models of dry tensile strength, wet tensile strength and degradation period at

 y1*=*30.38+9.135×10-3x1+5.4x2-1.52x3+0.067x4+0.94x5-1.02x12-0.64x42-1.15x52+ 1.14x1x4+ 1.24x2x3+0.96x3x4-1.11x4x5 (3-1)

+1.67x2x4+1.41x4x5 (3-3)

x3x5+0.65x4x5 (3-2)

2-1.32x32-0.87x42-0.87x5

2

y2=13.81-0.36x1+2.47x2-0.35x3-0.36x4+1.43x5-0.62x42-0.42x52+0.64x1x3+0.46x2x5-0.44

α=0.05, were significant and the models were shown as equation 3-1, 3-2 and 3-3.

which was defined degradation period. The result was shown in table 3-2.

y3*=*34.95+0.22x1+3.59x2+0.017x3+0.5x4+2.33x5-1.12x12-1.07x2

(c) part of film samples after 50 days

(a)part of film samples after 20 days

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degradation.

**3.2 Response model 3.2.1 Response model** 
